The technical scope of the present invention that of mechanical linking devices between a first and second mechanical element, such devices being pyrotechnically releasable.
Such devices are known notably in the field of automobile safety devices.
For example, patent DE19515852 discloses a device permitting two ends of a control rod of a master automobile brake cylinder to be pyrotechnically separated. Such a separation occurs in the event of an accident so as to avoid the brake pedal impacting on the driver""s ankles.
The separation device disclosed by this document implements a pyrotechnic charge arranged in a housing provided in the rod or else in a coupling sleeve between two elements forming the rod.
Separation devices are also known that implement what is commonly known as explosive bolts. Patent DE19515852 also discloses this solution, which is classically employed in separation devices used on ballistic or aeronautic vehicles.
The disadvantage of these solutions lies in that they are based on the high explosive effect of a pyrotechnic charge. Indeed, one or several primary explosives are used possibly in association with one or several secondary explosives or energetic but highly confined substances.
However, primary explosive are sensitive materials, which are thus difficult or hazardous to implement.
So as to ensure the fracture of mechanical support parts, the quantities of pyrotechnic charge necessary are also substantial ( greater than 100 mg), thereby further increasing the risks and the cost.
Known explosive bolts or other high explosive systems are thus unsuited to civil applications, notably in the area of the automobile.
Moreover, known bolts constitute locking means that are inserted transversally with respect to the elements to be joined. When the bolt is ignited, there is a risk of fragments of it remaining caught in the different elements thereby perturbing their detachment or separation. The separation effort of the two elements is thus non-reproducible and the device is not reliable enough unless an unacceptably large quantity of explosive is used.
Another device is also known by patent DE19617372 that allows two ends of a control rod for a master automobile brake cylinder to be pyrotechnically separated.
In this device the master cylinder rod is made integral in translation with the control pedal by means of a ring placed in a groove. This ring is expelled by the tensile or compressive forces exerted on the rod and it is held in the locking position by retention means that are formed by a piston pushed by a spring.
So as to ensure separation, a pyrotechnic charge is ignited that generates gases acting on the piston against the action of a spring.
The gases are also directed towards a chamber where they exert a force tending to separate the elements to be unlocked.
Such a device has a first disadvantage in that its structure is complicated and comprises numerous mobile parts and notably springs whose mechanical characteristics are likely to deteriorate over time.
This structure is thus likely to become stuck, and it also implements a large quantity of pyrotechnic composition acting notably on the mechanical elements to be unlocked so as to release the locking ring.
The gas generator is ring-shaped and is thus difficult to manufacture and integrate.
Moreover, as the effect of the gases is to act directly on the locking means, this results in a total loss of the possibility of acting on the master cylinder rod in the event of the pyrotechnic component being inadvertently ignited.
In the absence of an accident context, the triggering of the device results in the total loss of the braking capability.
Patent DE-A-4 305 049 describes a device which allows the retraction of the steering column thanks to the gas pressure produced by a pyrotechnic component. This component is applied against a firing pin by a spring and the ignition is achieved after its freeing by a bolt stopped by a sliding ring.
The aim of the invention is to propose a pyrotechnically releasable mechanical linking device for two mechanical elements that does not suffer from such drawbacks.
The pyrotechnically releasable mechanical linking device according to the invention is simple, compact and inexpensive in structure. It is simple to implement and permits the use of only a reduced quantity of pyrotechnic composition, such composition possibly being devoid of any primary explosive at all. In practical terms, the mass of composition alone contained in a pyrotechnic igniter for automobile safety systems can be used.
A standard pyrotechnic igniter can moreover be easily integrated inside the device according to the invention and this with no modification to its structure.
Additionally, the device according to the invention is reliable and ensures good reproducibility of the separation efforts of the mechanical elements.
The invention thus relates to a pyrotechnically releasable mechanical linking device between a first and second mechanical element, said first and second elements likely to be subjected to tensile and/or compressive force along an axis, said device comprising at least one pyrotechnic component and at least one locking means linking the two mechanical elements along at least one axis, said locking means able to be released when the mechanical elements are subjected to tensile and/or compressive forces along said axis and that is held in its locking position by retention means that are released by the pressure of gases generated by igniting the pyrotechnic component, device wherein the retention means comprise a cap integral with a head carrying the pyrotechnic component or else forming a head in itself carrying the pyrotechnic component.
According to one characteristic of the invention, the device incorporates a chamber in which the gases generated by the pyrotechnic composition develop, said chamber delimited on one a side by a bottom of a bore in the head and on the other by one end of the second mechanical element.
According to a first embodiment, the locking means are constituted by at least two balls housed in holes arranged in a tubular sleeve integral with the first of the two mechanical elements that co-operate with a groove integral with the second mechanical element, said balls being held in place by the cap that is able to move so as to release the balls further to the pressure of the gases generated by the pyrotechnic component.
The cap can be held axially with respect to the tubular sleeve by annular crimping of one of its ends onto the sleeve.
According to a second embodiment, the locking means are constituted by at least two jaws pressing on the first mechanical element and gripping one end of the second mechanical element, said jaws having a profile matching that of said end and held in place by the cap.
The cap can be held axially with respect to the tubular sleeve by annular crimping of one of its ends onto the jaws.
According to a variant embodiment, the jaw profile can be a tapping profile intended to co-operate with a threaded end integral with the second mechanical element.
The jaws can be held by a flexible ring before the cap is attached.
Advantageously, each jaw may have an external profile incorporating at least one flat part, the assembled jaws forming a nut.
The device can incorporate a spacer ring surrounding an end of the pyrotechnic component and incorporating an abutment surface for the threaded end integral with the second mechanical element so as to avoid any contact of the latter with the pyrotechnic component.